The present invention relates to a method of writing tracks on a magnetic disc with signals for positioning a magnetic writing/reading head, which is included in a magnetic disc drive unit, and a device for executing said method.
These days, recording density of magnetic discs have been higher and higher, so the servo tracks must be correctly written thereon. The servo tracks are usually written in manufacturing factories, so time of writing the servo tracks must be shorter so as to improve manufacturing efficiency.
Usually, a plurality of the magnetic discs are accommodated in the magnetic disc drive unit and they are coaxially fixed to a spindle. In each magnetic disc, a plurality of servo tracks are coaxially written like concentric circles, and the signals for positioning the magnetic head are written on the servo tracks. In a factory, the magnetic disc drive unit is assembled and the servo tracks are written on the magnetic discs, by a device for writing the servo tracks, before the magnetic discs are tightly accommodated in the magnetic disc drive unit.
A basic structure of the magnetic disc drive unit will be explained with reference to FIG. 13.
The magnetic disc drive unit 50 comprises: the magnetic discs 52, which are rotated; the magnetic heads 54 for writing data on and reading data from the magnetic discs 52; and an inner actuator 56, which moves the magnetic heads 54 in substantially radial direction of the magnetic discs 52.
Next, a conventional device 58 for writing the servo track on the magnetic discs 52 of the magnetic disc drive unit 50 will be explained.
An external actuator 60 is provided outside of the magnetic disc drive unit 50. The external actuator 60 is capable of moving along a moving track of the inner actuator 56.
The external actuator 60 includes a displacement sensor 62, which is capable of detecting amount X.sub.1 of displacement between the external actuator 60 and the inner actuator 56. To detect the amount X.sub.1 of the displacement without touching, an optical reflector 64, e.g., a cylindrical mirror, for example, is attached to the inner actuator 56; the displacement sensor 62 is an optical sensor, which is capable of emitting light to the optical reflector 64 and receiving the reflected light therefrom, so that it detects the amount of displacement between the optical reflector 64 and the displacement sensor 62.
With this structure, the displacement sensor 62 is capable of detecting the amount of displacement between the optical reflector 64 and the displacement sensor 62, and the detected amount of the displacement is the amount X.sub.1 of the displacement between the external actuator 60 and the inner actuator 56.
The device further has: a position sensor 66 detecting a present position Y of the external actuator 60; a destination setting section setting a travel destination Y.sub.0, at which the inner actuator 56 is located when the magnetic heads 54 are located at object positions; and a first control section 70 moving the external actuator 60 to the travel destination Y.sub.0 by checking deviation X.sub.3 between the present position Y of the external actuator 60, which is detected by the position sensor 66, and the travel destination Y.sub.0, and controlling the movement of the external actuator 60 to maintain the deviation X.sub.3 within a predetermined range A. A non-touch type optical sensor, for example, is employed as the position sensor 66 as well as the displacement sensor 62, and the position sensor 66 comprises: an optical reflector 66b attached to the external actuator 60; and an optical sensing member 66a capable of emitting light to the optical reflector 66b and receiving the reflected light therefrom to measure distance to the optical reflector 66b as amount of moving the external actuator 60, e.g., rotational angle.
In the conventional device, voice coil motors are employed in the inner actuator 56 and the external actuator 60 as one example. Actuator arms 56a and 60a are respectively provided to the actuators 56 and 60 to move the magnetic heads 54 and the displacement sensor 62 in substantially radial direction of the magnetic discs 52, and the arms 56a and 60a are capable of rotating about a common axis L. With this structure, the external actuator 60 is capable of moving along a moving track (an arc-shaped track) of the inner actuator 56. The reflector 64 and the displacement sensor 62 are respectively attached to the actuator arms 56a and 60a with the same distance from the axis L, so the reflector 64 and the displacement sensor 62 are capable of moving on the same circular track around the axis L. The voice coil motor 60b is provided in the external actuator 60 to rotate the actuator arm 60a.
A second control section 72 controls the inner actuator 56 to make the amount X.sub.1 of displacement equal to a predetermined value B. Concretely, a predetermined range (an allowable error range) .lambda. is previously set, and the second control section judges the amount of the displacement is equal to the predetermined value B if .lambda..gtoreq..vertline.X.sub.1 -B.vertline.. On the other hand, the second control section judges the amount X.sub.1 of the displacement is not equal to the predetermined value B if .lambda.&lt;.vertline.X.sub.1 -B.vertline.. In the case of .lambda.=0, the second control section 72 controls the inner actuator 56 to follow the movement of the external actuator 60 so as to satisfy the formula .lambda..gtoreq..vertline.X.sub.1 -B.vertline.. The predetermined value B is inputted to the second control section 72 by a setting section 74.
In the conventional device, the first and the second control sections 70 and 72 include: a first adjusting unit 76 and a second adjusting unit 78, each of which outputs signals corresponding to difference between two inputted signals; and a first amplifier 80 and a second amplifier 82, which amplify the output signals of the adjusting units 76 and 78 and which output first signals and second signals for driving the inner actuator 56 and the external actuator 60.
With above described structure, the first control section 70 moves the external actuator 60 to and positions the same at the travel destination Y.sub.0 by inputting the travel destination Y.sub.0 in the destination setting section 68 of the servo track writing device 58.
Then the inner actuator 56 is controlled to follow the external actuator 60 and positioned at the travel destination Y.sub.0.
The action will be described in detail with reference to FIG. 14. The travel destination Y.sub.0 is inputted (Step 100); the position sensor 66 always detects the present position Y of the external actuator 60 (Step 102); the deviation X.sub.3 between the travel destination Y.sub.0 and the present position Y, i.e., X.sub.3 =Y.sub.0 -Y, is detected; and the absolute value of the deviation X.sub.3 is checked to determine if it is in the predetermined range A or not (Step 104).
If the absolute value of the deviation X.sub.3 is not in the standard range A, the external actuator 60 is moved toward the travel destination Y.sub.0 (Step 102), and the step flow returns to Step 102. By repeating Steps 102-106, the absolute value of the deviation X.sub.3 (=.vertline.Y.sub.0 -Y.vertline.) is gradually reduced. When the value is in the standard range A, the external actuator 60 is judged to reach the travel destination Y.sub.0, and the step flow returns to Step 102 without moving the external actuator 60.
The action will be explained in detail with reference to FIG. 15. The displacement sensor 62 inputs the amount X.sub.1 of the displacement between the inner actuator 56 and the external actuator 60, i.e., the displacement between the displacement sensor 62 and the optical reflector 64 (Step 200). Then the amount X.sub.1 of the displacement is compared with the predetermined value B to judge if the deviation .vertline.X.sub.1 -B.vertline. is within the standard range .lambda. or not (Step 202). In other words, the amount X.sub.1 of the displacement is checked if it satisfies the formula B- .lambda..ltoreq.X.sub.1.ltoreq.B- .lambda. or not. Actually, B=0 and .lambda.=0 so the amount X.sub.1 of the displacement is checked to determine if the amount X.sub.1 is zero or not.
If the amount X.sub.1 of the displacement is not zero, the inner actuator 56 is moved toward the external actuator 60 (Step 204), and the step flow returns to Step 200. By repeating Steps 200-204, the inner actuator 56 is moved close to the external actuator 60. If the amount X.sub.1 of the displacement is equal to the predetermined value B, the inner actuator 56 is judged to reach the external actuator 60, so the step flow returns to Step 200 without moving the inner actuator 56.
By the above described action, the external actuator reaches the travel destination Y.sub.0, then inner actuator 60 also reaches the same travel destination Y.sub.0. With this action, the magnetic heads 54, which are moved in substantially radial direction of the magnetic discs 52, are positioned at the object positions. Then the servo track signals are written on the tracks of the magnetic discs 52, in which the object positions are included, with the magnetic heads 54.
However, in the conventional servo track writing device 58, the external actuator 60 is controlled on the basis of the inputted travel destination Y.sub.0. And, as shown in FIG. 16, the inner actuator 56 is always controlled to follow the external actuator 60 and to move toward the present position Y of the external actuator 60, which precedes the inner actuator 56 and moves to the travel destination Y.sub.0, as an object.
With this action, there is a disadvantage in that the external actuator 60 is positioned prior to the inner actuator 56, so time for positioning the inner actuator 56 is always longer than that for positioning the external actuator 60. 56, so time for positioning the inner actuator 56 is always longer than that for positioning the external actuator 60.
While the magnetic heads 54, which have been positioned at the object positions, write the servo track signals, it is necessary to prevent vibration of the magnetic heads 54.
The vibration is caused by operator's action for operating the device 58 or conducted via a floor on which the device 58 is installed. In any case, the device 58 is vibrated and the vibration is conducted to the magnetic disc drive unit 50, which has been connected with the device 58.
However, in the conventional device 58, the inner actuator 56 is controlled to follow the present position of the external actuator 60, so the inner actuator 56 is vibrated as well as the external actuator 60 when the external actuator 60 is vibrated. Amplitude of the vibration of the inner actuator 56 is equal to that of the external actuator 60; by considering overshoot and undershoot, the amplitude of the inner actuator 56 is greater than that of the external actuator 60. By the vibration, quality of the written servo track signals will be worse.